Not sure about variants, though it was certainly typical of politically inflected songs of his era being adapted somewhat to suit certain situations. There are about 4 versions of "Jarama Valley," for example. My father told me he was very close to the song when he heard the recording of Pasiones, and did say at one point that he was the first to sing it, but i don't think he ever recorded it, and I have no other evidence that he was the first singer except for his anecdote. (He was certainly captivated by FDR and his policies, and had sung at the White House for the staff there - the workers, not the political people - with the Priority Ramblers at Eleanor's invitation.) Place a song like that in a specific context, as it was in Pasiones, and it immediately speaks to the loss of a comrade in Spain, and for some who knew it in connection to FDR, it might have carried traces of both losses. I do find the line "The fight will go on 'til we win" very resonant with the Spanish conflict and the anti-fascist struggle, whether the song was written to that purpose or not.